The embodiments described herein relate generally to power generation, and more specifically, to methods and systems for controlling an intra-plant voltage level within a renewable energy based power plant.
Light and wind are examples of renewable sources of energy that are increasingly becoming attractive alternative sources of energy. Solar energy in the form of sunlight may be converted to electrical energy by solar cells. A more general term for devices that convert light to electrical energy is “photovoltaic cells.” A plurality of solar cells may be coupled together into solar modules. Solar modules may also be coupled together to provide a desired level of power, which is referred to herein as a solar farm. Wind energy may be converted to electrical energy using a wind turbine generator. Wind turbine generators typically include a rotor having multiple blades that transform wind energy into rotational motion of a drive shaft, which in turn is utilized to drive an electric generator. A plurality of wind turbine generators may be coupled together to provide a desired level of power and are referred to herein as a wind farm.
Power plants, including solar farms and wind farms, typically deliver their produced power to customers over an electrical grid. Electricity applied to the electrical grid is required to meet grid connectivity expectations. These requirements address safety issues as well as power quality concerns. For example, the grid connectivity expectations include operating the power generation system during a transient event, also referred to herein as a grid fault event. This capability may be referred to as low voltage ride through (LVRT) or zero voltage ride through (ZVRT). An LVRT/ZVRT event is a condition where the alternating current (AC) utility voltage is low on either one phase of the electrical grid or multiple phases of the electrical grid. During an LVRT/ZVRT event, the capacity of the electrical grid to accept power from the power generation system is low, a condition also referred to herein as a “weak grid”.
Furthermore, the efficiency of the power conversion performed by inverters included within typical solar farms and wind farms is dependent upon the grid voltage. The grid voltage is not constant, but rather, may vary depending on, for example, other loads coupled to the electrical grid and/or other power generation systems coupled to the electrical grid. Typically, a solar farm is expected to provide full power without curtailments when the grid voltage is within a predefined tolerance of a nominal grid voltage. For example, a regulation may include a requirement that a solar farm coupled to the electrical grid provide full power to the electrical grid when the grid voltage is ±10% of the nominal grid voltage. The predefined tolerance may also be higher, for example, ±15-20% of the nominal grid voltage. Typical solar farm and wind farm inverters require a wide voltage tolerance band in order to provide power that matches the varying grid voltage. The wide grid voltage range limits the efficiency of the power conversion performed by solar/wind farm inverters and may increase the cost of the solar/wind farm inverters.